We are studying the mitochondrial DNA from Crithidia fasciculata known as kinetoplast DNA. This DNA is in the form of thousands of minicircles and a few maxicircles linked together in a massive network. We have previously shown that minicircles replicate after release from the networks and the progeny are reattached. Presumably release and reattachment are catalyzed by a topoisomerase and we are purifying and characterizing the enzyme. We are also studying maxicircle replication to learn whether these molecules replicate by a mechanism similar to that of minicircles. We are also studying the structural organization of networks using electron microscopy, restriction enzyme analysis, DNA sequencing, and decatenation by topoisomerases.